Studies of diet and health focus increasingly on dietary patterns. Although the traditional Mediterranean diet is perceived as being healthy, there is little information on its possible benefit to young people. We studied whether closer adherence to the traditional Mediterranean dietary pattern was associated with overall and cancer mortality in a cohort of 42237 young women, aged 30–49 years at enrolment, who were recruited in 1991–2 from the general population in the Uppsala Health Care Region, Sweden, and followed up, almost completely, for about 12 years. Adherence to the Mediterranean diet was assessed by a 10-point score incorporating the characteristics of this diet. Among women less than 40 years old at enrolment – whose causes of death are mainly cancer with probable genetic influences, injuries or suicide – there was no association of the Mediterranean diet score with total or cancer mortality. Among women 40–49 years old at enrolment, a 2-point increase in the score was associated with considerable reductions in overall mortality (13%; 95% CI 1%, 23%; P0·05) and cancer mortality (16%; 95% CI −1%, 29%; P0·06). Few cardiovascular deaths occurred in this cohort of young women. The findings of the present study in a northern European population of young women indicate that closer adherence to a Mediterranean dietary pattern reduces mortality even among young persons.